Low grade gliomas (LGGs) are generally located in the temporal lobe.
With the advance of genomics research, there have been a new breakthrough in the molecular classification of gliomas. Glioblastoma (WHO grade Ⅳ) could be subtyped to proneural, neural, classical, and mesenchymal according to the mRNA expression. Low grade gliomas (WHO grade Ⅱ and Ⅲ) could be divided into 5 types using 1p/19q co-deletion, isocitrate dehydrogenase(IDH) mutation, and TERTp (promotor region) mutation. In 2016, a new classification of tumors of the central nervous system was proposed, and some new markers such as IDH1 mutation were introduced into the diagnosis of gliomas. Genotype and phenotype were integrated to diagnose gliomas. In the meantime, precision treatment for gliomas has also been vigorously developed 1).
With the increased understanding of glioma tumour genetics there is a need to understand the changes and their implications for patient management. There has also been an increasing trend for adopting earlier, more aggressive surgical approaches to low grade glioma treatment 2).
Verma and Mehta et al., discuss the recent genomics of gliomas, and also the results of seminal LGG trials in the context of molecular and genomic stratification, with respect to both prognosis and response to therapy.
They also analyze implications of these “molecular classifications”. They propose separating out the worst prognostic subsets, whose outcomes resemble those of glioblastoma patients. Lastly, a brief discussion is provided regarding translating this collective knowledge into the clinic and in treatment decisions; also addressed are some of the many questions that still need to be examined in light of these strong and emerging data 3).
They include a number of subtypes:
and mixed tumours, e.g. oligoastrocytoma
The term should not be used for a specific, non-infiltrative WHO I tumour of astrocyte-lineage such as pleomorphic xanthoastrocytoma (PXA), subependymal giant cell astrocytoma (SGCA) and pilocytic astrocytoma, as these have different prognosis, treatment and imaging features.
The most critical molecular alterations (IDH1/2, 1p/19q codeletion, ATRX, TERT, CIC, and FUBP1) and circumscribed (BRAF-KIAA1549, BRAF(V600E), and C11orf95-RELA fusion) gliomas. These molecular features reflect tumor heterogeneity and have specific associations with patient outcome that determine appropriate patient management. This has led to an important, fundamental shift toward developing a molecular classification of World Health Organization grade II-III diffuse glioma 4)
Preoperative seizures could reflect intrinsic glioma properties 5).
The results of a genomic analysis suggest that low FOXO4 expression is a significant risk factor for epileptic seizures in patients with LGGs and is associated with the seizure outcome. FOXO4 may be a potential therapeutic target for tumor-associated epilepsy 10).
Arterial spin labelled imaging, DTI, and Proton magnetic resonance spectroscopic imaging are useful for predicting glioma grade. Additionally, the parameters obtained on DTI and MR spectroscopy closely correlated with the proliferative potential of gliomas 11).
The Apparent Diffusion Coefficient (ADC) values of low-grade (WHO I-II) glioma were higher than that of high-grade (WHO III-IV), but the cell density of low-grade glioma was apparently lower than that of high-grade glioma. The ADC values and density of tumor cells were negatively correlated with WHO malignant grades, while the density of cells of glioma was positively correlated with WHO malignant grades 12).
Usually, low grade gliomas show no increase in tumor rCBV, whereas high grade gliomas demonstrate high relative cerebral blood volume (rCBV) that in some cases even extends outside the contrast-enhancing portions of the tumor 13).
A retrospective consecutive assessment of patients treated for LGGs (World Health Organization grade II) with iMRI-guided resection at 6 neurosurgical centers was performed. Eloquent location, extent of resection, first-line adjuvant treatment, neurophysiological monitoring, awake brain surgery, intraoperative ultrasound, and field-strength of iMRI were analyzed, as well as progression-free survival (PFS), new permanent neurological deficits, and complications. Multivariate binary logistic and Cox regression models were calculated to evaluate determinants of PFS, gross total resection (GTR), and adjuvant treatment.
A total of 288 patients met the inclusion criteria. On multivariate analysis, GTR significantly increased PFS (hazard ratio, 0.44; P < .01), whereas “failed” GTR did not differ significantly from intended subtotal-resection. Combined radiochemotherapy as adjuvant therapy was a negative prognostic factor (hazard ratio: 2.84, P < .01). Field strength of iMRI was not associated with PFS. In the binary logistic regression model, use of high-field iMRI (odds ratio: 0.51, P < .01) was positively and eloquent location (odds ratio: 1.99, P < .01) was negatively associated with GTR. GTR was not associated with increased rates of new permanent neurological deficits.
GTR was an independent positive prognostic factor for PFS in LGG surgery. Patients with accidentally left tumor remnants showed a similar prognosis compared with patients harboring only partially resectable tumors. Use of high-field iMRI was significantly associated with GTR. However, the field strength of iMRI did not affect PFS 15).